A range in which read reference voltages in multi-level cell flash memory can be set is referred to as a voltage sweep window. Due to implementation limitations and other considerations by the flash memory manufactures, the range is often limited by a narrow voltage sweep window around a default value. Even if the voltage sweep window is wide enough, considerable degradation of flash cell quality, voltage drift by retention effects and read disturb can move a preferred read voltage setting outside the voltage sweep window. For other situations, the various factors make the preferred read voltage too close to the edges of the voltage sweep window or too close to unreliable regions of the possible range. As a result, an ability to use more read voltages around the preferred read voltage in read retries is effected.